The invention relates to a film for blinds, the particular purpose of which is to act as a movable cover for panes of glass, as well as to a process for production of the same.
Blinds for darkening, shading or decorating windows have already been disclosed in the past. In their basic form they consist of a rotating roller located at the top to wind the actual blind either up or down, the bottom end of the blind being stabilised and weighted by a stiffening element such as a rod. The material used for the blind can, for example, be a 0.3 mm thick film, while the roller has a diameter of 30 mm. In the case of manually actuated blinds, a cord of some sort is generally attached to the end stiffening element and the roller is driven by a spring-loaded device. In the case of electric blinds, the drive generally act; on the roller.
Specially designed blinds can also act as movable heat protection for windows, house facades or solar collectors with a view to controlling the heat flow. DT 2446203, for example, proposes a solution for the thermal protection of windows and suitable protective films are described in EP 0483528A1. They generally consist of a thin plastic film laminated with copper or aluminium in such a way that they are, for example, semi-transparent to light but still reflect heat radiation almost completely. Their conventional internal location does, however, cause problems, because a window pane located behind the heat protection film forms condensation and steams up in cold weather.
The potential application for automatically controlled blinds with windows and house facades in particular have, for example, been investigated by the Fraunhofer Institute for Solar Energy Systems in Freiburg im Breisgau/Germany. The results show that they help to save considerable amounts of heating energy and that solar energy can be exploited with them. One of the systems disclosed makes use, for example, of specially designed windows in which a heat-effective blind is located between panes of glass. It is, however, a rather laborious and costly process to produce and assemble such windows, so that they do not satisfy market requirements.
Since the overwhelming majority of windows nowadays are fitted with double (or triple) glazing, it is a logical solution to locate blinds in the space between the panes of glass. Extremely compact blinds with a depth of only 16 to 22 mm are, however, required for this purpose. Proposals for solutions can be found, for example, in the patents EP 0154218A2 and EP 0483528A1 and products of this kind are also available on the market. They do, however, have their shortcomings, which are quite considerable in some cases. It can even be observed that demonstration models at trade fairs, shows and exhibitions are sometimes fitted with protective films that wind up crookedly, form wrinkles, do not hang straight or even stick to the pane of glass. It is evident that the technical problems which arise with an extremely compact blind have not yet been solved fully satisfactorily.
The objective of the invention is to create a blind that does not have the shortcomings and disadvantages outlined above, that is suitable for installation between the panes of windows with double (or triple) glazing and that can be produced inexpensively.
This objective is achieved by a film for blinds and a process for production of the same in accordance with claim 1.
A film for blinds in accordance with the invention has creases at an angle of up to 180 degrees that extend in the same direction parallel to the winding axis of the blind. Due to their flexural moment, these creases lead to the formation of a wave profile, that in turn forms a roll with a cross-section similar in shape to a sprocket wheel and with its own torque when the blind is wound up and all the layers are resting directly on top of each other. A film for blinds that is designed in this way has a number of outstanding properties, the most important of which are listed below:
1. The blind winds up tidily and accurately because the layers rest directly on top of each other when the blind has been rolled up.
2. The crease torque facilitates the blind winding operation.
3. The wave profile helps to increase transverse stiffness.
4. A cushion of air is formed, which stops the blind sticking to the pane of glass.
A blind consisting of the film for blinds in accordance with the present invention and a winding mechanism can be used for the conventional purpose of decorating or shading windows. In such cases the film for blinds can be produced from materials and by processes that are used for pleated blinds. As is generally known, such pleated blinds have narrow folds in a zigzag pattern similar to the equidirectional creases required in the film for blinds. It is possible to produce these creases in a simple way by a special process, in the course of which a round roll is formed into a flattened roll.
When the blind is used for heat protection purposes, the preferred location is between the panes of windows with double (or triple) glazing. In view of the protected location, the film for blinds can be designed to be extremely thin and light, with the advantage that the capacity of the drive provided to wind up and unwind the blind only needs to be very small. Practical experience to date has shown that a battery-driven electric motor with a capacity of 0.3 W is sufficient to drive such a blind. The low power requirement means that the blind can also be actuated by a magnetic device that transmits force or torque from the outside to the inside through one of the panes of glass to move the blind. In a preferred embodiment, the blind is actuated manually in the space between panes of glass by moving the magnetic device. The magnetic device can of course also be used to transmit force in the case of an electric drive located externally.